Pyompa

Corresponds to PR https://github.com/nitrogenlab/pyompa/pull/8

Corresponds to PR https://github.com/nitrogenlab/pyompa/pull/6

For Zenodo release, creating a tag corresponding to the current dev branch

(Evidently forgot to create a tag for this earlier). Corresponds to PR https://github.com/nitrogenlab/pyompa/pull/4; description of changes reproduced here.

- Added support for "depth_default" in the penalty functions
- Rows with na values in the parameter columns for the observations are automatically dropped
- If an endmember name for which a usage penalty is specified is not in the endmembers df, an error now gets thrown

Corresponds to pull request https://github.com/nitrogenlab/pyompa/pull/3

Fixes:
- Fixed bug where column with endmember names had to be called "endmember_name"
- More informative error messages

New features:
- Can take in a list of configuration files (which are concatenated under the hood)
- plot_ompaproblem_endmember_usagepenalties now called plot_ompasoln_endmember_usagepenalties, and can accept an ompasoln object
- Plot of oxygen deficit as well as the plot of parmameter residuals use a diverging colormap; actual parameter residuals (not just absolute value) are now plotted.

Notebook: https://colab.research.google.com/github/nitrogenlab/GP15_watermassanalysis/blob/9eeca86f34d647e633c5b590416b7cd50acb1de6/config_files_demo.ipynb

Corresponds to PR https://github.com/nitrogenlab/pyompa/pull/2